1. Field of the Invention
The present invention refers to a vertical conveying apparatus with a lifting unit guided in two guiding rails and with an emergency brake which influences the lifting unit as soon as a preselectable lifting speed is exceeded, to decrease the speed of the lifting unit. Such an apparatus is intended to work at high speed and acceleration even if the lifting unit is heavily loaded and must provide absolute safety against damage and accidents as a consequence of too high a lifting speed of the lifting unit.
2. Description of the Prior Art
For emergency brakes to be used with such apparatus or with elevators for humans, which are used to switch off the driving gear and to safely stop the lifting unit, it is imperative to provide a system which works absolutely reliably and effectively. The emergency braking systems known in the prior art work abruptly inasmush as a braking wedge provided with a toothed surface is suddenly pressed against a guiding or braking rail, whereby it often happens that the tooths of the braking wedge damage the surface of the guiding or braking rail, which is then ruined and subject to re-machining or replacement. The braking effect is very abrupt and the releasing of the braking system is sometimes very difficult. If the lifting unit is heavily loaded or subjected to a great acceleration or deceleration, there occurs the danger that passengers on the lifting unit may be severely injured by the sudden stop common to the emergency braking systems of the prior art. This danger can only partially be avoided by overdimensioning the driving and braking system.
If an automatic position coding system is used with such an apparatus, it may happen that the lifting unit stops between two distance marks if the emergency braking system is activated, thereby rendering it impossible to determine the actual position of the lifting unit by means of the remote control system.